Is she charging for the cancelled session, the final shortened session, or future appts? I have experienced the frustration of being billed for a termination session in which she made an egregious, life-threatening error and used the session to explain why it wasn't her fault. I ended up walking out early. When she had the nerve to send me a bill, I felt it was easier to pay and be done with her forever.

You should not be billed for sessions you cancelled with a 24-48 hr warning or for any sessions she may feel you contractually owe her in the future.

Good luck.